Kiwifruit Growth Research Articles

Overexpression of the Kiwifruit Transcription Factor AaMYB44 Decreases the Cold Tolerance in Arabidopsis thaliana

Cold stress is one of the main abiotic stresses that affect the development and growth of kiwifruit (Actinidia arguta). Herein, we analyzed the transcriptomic data of A. arguta dormant shoots in response to low-temperature treatment, identified 52 MYB genes, and constructed a phylogenetic tree based on the encoded protein sequences. Then, the effect of one MYB gene on cold tolerance was analyzed. This gene had an open reading frame of 837 bp long and encoded 279 amino acids. Sequence alignment and phylogenetic analysis revealed that this gene belongs to the R2R3-MYB family and was named AaMYB44 based on its homology to other MYB family members. Quantitative real-time PCR revealed that AaMYB44 expression was significantly induced by low temperatures but exhibited the opposite trend in cold-tolerant genotypes. Subcellular localization assays revealed the nuclear localization of the AaMYB44 protein. Furthermore, AaMYB44 was transformed into Arabidopsis thaliana (A. thaliana) via inflorescence infection, and physiological and biochemical tests revealed that the cold resistance and antioxidant capacity of the transgenic A. thaliana were lower than those of wild-type plants. Overall, AaMYB44 might play a negative regulatory role in response to cold stress, providing new insight into the mechanism of cold tolerance.

Metallothionein family genes in kiwifruit: characterization and determining their roles in plant's response to different stresses.

Kiwifruit growth and development are severely affected by various biotic and abiotic stresses, especially cold stress and the bacterial disease caused by Pseudomonas syringae pv. actinidiae (Psa). Metallothioneins (MTs) are a group of cysteine-rich proteins that play crucial roles in stress response, metal detoxification, and homeostasis in plants. However, the protective role of these MTs in kiwifruit remains to be elucidated. In the present study, four AcMT genes were identified in the Hongyang kiwifruit genome, namely, two Type 2 isoforms (AcMT2 and AcMT2a) and two Type 3 isoforms (AcMT3a and AcMT3b) located separately on four different chromosomes. The hormones and stress response cis-elements within the promoter regions of these AcMTs were characterized. It was revealed that the four AcMT genes exhibited different expression patterns in different tissues: AcMT2 and AcMT2a were expressed at much higher levels in the fruit, male flower, female flower, root, and bark, while AcMT3a was expressed mainly in the fruit and AcMT3b was expressed highly in the bark. The expression patterns of these AcMT genes after exposure to Psa infection and different phytohormones, including gibberellic acid A3(GA3), ethylene (ET), and abscisic acid (ABA), were evaluated. It was revealed that in response to Psa infection, the main AcMTs in each tissue (those with expression levels higher compared to the other MTs in that tissue) were downregulated during the early stage in kiwifruits, followed by a recovery phase. In addition, most AcMTs were downregulated after exposure to ET and GA3, while type 2 AcMTs (AcMT2 and AcMT2a) were upregulated after treatment with ABA. The overexpression of AcMTs in Escherichia coli presented a higher tolerance to H2O2, heavy metals, low temperature, and high temperature. Collectively, these findings demonstrated the protective roles of AcMTs in terms of stress resistance conferred through plant hormone-related signal pathways.

Appraisal of extended cane length and fruit thinning strategies on the performance of growth yield and quality of kiwifruit

The kiwifruit has been identified as an enormous fruit for mid-hill horticulture due to its wider adaptability and diversification. The size and quality of kiwifruit were affected by its market. As a result, appropriate canopy management and orchard techniques are key components in its production. Pruning and hand thinning, especially in kiwifruit, have been observed to improve the size and quality of the fruit. Traditional pruning maintained shorter canes with 6–12 nodes and 4 fruits/shoots. However, this study extended cane length and retained loads of 20 nodes/cane and 6 fruits/shoot. Considering the above, a study was conducted to determine the effects of extended cane length and fruit thinning on kiwifruit growth, yield, and fruiting performance. Five pruning levels have been employed: 8, 10, 12, 14, and 16 nodes/cane; 4, 6, and 8 fruits/fruiting shoot. The result revealed that the pruning of up to 12 nodes/cane coupled with thinning up to 6 fruits/fruiting shoot resulted in maximum cane diameter, leaf area, leaf: fruit ratio, advancement in flower initiation, bud break percentage (86.79 %), real fertility index, fruit yield and a proportion of grade “A" fruits. The highest leaf chlorophyll content (67.50), flowers per floral shoot, and productivity were recorded with pruning up to 16 nodes/cane coupled with thinning up to 6 fruits/fruiting shoot. The physico-chemical parameters such as fruit weight, diameter, volume, TSS, TSS: acid ratio, total sugars, and C: N ratio of the leaf and shoot were also found to be highest with pruning up to 12 nodes/cane coupled with thinning up to 6 fruits/fruiting shoot. This treatment also gave the maximum net return on a per-hectare basis, hence it was found to be the most profitable for the farmers.

Design and experimentation of multi-fruit envelope-cutting kiwifruit picking robot.

Currently kiwifruit picking process mainly leverages manual labor, which has low productivity and high labor intensity, meanwhile, the existing kiwifruit picking machinery also has low picking efficiency and easily damages fruits. In this regard, a kiwifruit picking robot suitable for orchard operations was developed in this paper for kiwifruit grown in orchard trellis style. First, based on the analysis of kiwifruit growth pattern and cultivation parameters, the expected design requirements and objectives of a kiwifruit picking robot were proposed, and the expected workflow of the robot in the kiwifruit orchard environment was given, which in turn led to a multi-fruit envelope-cutting kiwifruit picking robot was designed. Then, the D-H method was used to establish the kinematic Equations of the kiwifruit-picking robot, the forward and inverse kinematic calculations were carried out, and the Monte Carlo method was used to analyze the workspace of the robot. By planning the trajectory of the robotic arm and calculating critical nodes in the picking path, the scheme of trajectory planning of the robot was given, and MATLAB software was applied to simulate the motion trajectory as well as to verify the feasibility of the trajectory planning scheme and the picking strategy. Finally, a kiwifruit picking test bed was set up to conduct picking tests in the form of fruit clusters. The results show that the average time to pick each cluster of fruit was 9.7s, the picking success rate was 88.0%, and the picking damage rate was 7.3%. All the indicators met the requirements of the expected design of the kiwifruit-picking robot.

Rapid and Visual Detection of Actinidia Chlorotic Ringspot-Associated Virus Using One-Step Reverse-Transcription Recombinase Polymerase Amplification Combined with Lateral Flow Dipstick Assay.

Actinidia chlorotic ringspot-associated virus (AcCRaV) occurs widely in major kiwifruit producing areas of China and is often accompanied by coinfecting viruses, affecting the growth, yield, and quality of kiwifruit. Therefore, a rapid and sensitive detection method is crucial for diagnosing and developing effective AcCRaV management strategies. In this study, a one-step reverse-transcription recombinase polymerase amplification combined with a lateral flow dipstick (RT-RPA-LFD) assay was developed for rapid detection of AcCRaV. Specific primers and a probe were designed based on the conserved region of the coat protein gene sequence of AcCRaV. The one-step RT-RPA reaction can be performed at 35 and 40°C within 10 to 30 min, and the amplification results can be read directly on the LFD within 5 min. The detection limit of the one-step RT-RPA-LFD assay was 10-8 ng (about 20 viral copies), which was equal with one-step RT-qPCR and 100 times more sensitive than one-step RT-PCR. Moreover, the one-step RT-RPA-LFD assay was successfully applied to detect AcCRaV from crude extracts, and the entire detection process can be completed within 40 min. These results indicate that the RT-RPA-LFD assay is a simple, rapid, and sensitive strategy that can be used for accurate diagnosis of AcCRaV-infected kiwifruit plants in the field. To our knowledge, this is the first study applying the one-step RT-RPA-LFD assay to detect a kiwifruit virus.

Genomic Colinearity and Transcriptional Regulatory Networks of BES1 Gene Family in Horticultural Plants Particularly Kiwifruit and Peach

The BES1 transcription factor family was unique and critical in plants. The BES1s played roles in the Brassinosteroid (BR) signaling pathway and participated in the plant’s development, maturation, and stress response process. This study investigated the function of the BES1 gene family of 48 horticultural crops by phylogenetic and genomic colinearity network analysis. In addition, the transcriptional regulatory networks had analyzed the process during biotic stress, abiotic stress, fruit development, and postharvest of kiwifruit and peach. The study illustrated a comprehensive understanding of the phylogenetic relationships of the BES1 family in plant genomes and the prediction of growth and development of kiwifruit and peach fruits and maturation-related BES1 members, laying the foundation for further functional studies of BES1 genes in the future.

Improvement of rooting and growth in kiwifruit (Actinidia deliciosa) cuttings with organic biostimulants

Seaweed extracts have shown profoundly positive effects on crop growth, quality and reproduction in diverse agricultural and horticultural crops. Seaweed extracts can be used to promote the rooting and growth of cuttings in perennial fruit species like kiwifruit (Actinidia deliciosa). In this study, the cuttings were treated with 1, 5, 10 and 50% solutions of G Sap (Gracilaria edulis), K Sap (Kappaphycus alvarezii), AN (Ascophyllum nodosum), EM (Ecklonia maxima), HA (Humic acid) and control (water) for 6 h as base dipping. Subsequently, the treatments of G Sap, K Sap, AN, EM, HA and control were repeated every 15 days for a period of six months as application of 50 ml solutions in the potted cuttings. All the treatments exhibited significant effects on the rooting percent in all the kiwifruit cultivars, namely ‘Monty’, ‘Abott’, ‘Hayward’, ‘Allison’ and ‘Bruno’ (P ≤ 0.01) as compared to the control. Shoot and root growth parameters including leaf number per cutting, number of roots per cutting, number of branches, plant height, shoot diameter, root length, root diameter and root weight were all positively increased with the application of seaweed extracts (P ≤ 0.05). Cuttings treated with seaweed extract exhibited significantly higher levels of pigments (chlorophyll a, chlorophyll b and total carotenoids), metabolites (total carbohydrates and soluble phenols) and less electrolyte leakage as compared to the control cuttings. Significant positive and negative correlations were observed between biochemical parameters combined with plant nutrient concentration. Principal component analysis (PCA) revealed that PC1 and PC2 (first two principal components) accounted for 75% of the entire variation. While, PC1 accounted for 63% of the total variation, PC2 accounted for 11% of the total variation. The leaves and the roots of kiwifruit cultivar ‘Hayward’ treated with G Sap at 10%, K Sap at 10%, AN at 10%, EM at 10%, HA at 10% exhibited higher expression of all four root promoting candidate genes (GH3-3, LBD16, LBD29 and LRP1) compared to the control. Therefore, it can be concluded that, seaweed extract and humic acid can be used as a suitable alternative to synthetic hormones for promoting the rooting and growth of kiwifruit cuttings.

A comprehensive metabolic map reveals major quality regulations in red-flesh kiwifruit (Actinidia chinensis).

Kiwifruit (Actinidia chinensis) is one of the popular fruits world-wide, and its quality is mainly determined by key metabolites (sugars, flavonoids, and vitamins). Previous works on kiwifruit are mostly done via a single omics approach or involve only limited metabolites. Consequently, the dynamic metabolomes during kiwifruit development and ripening and the underlying regulatory mechanisms are poorly understood. In this study, using high-resolution metabolomic and transcriptomic analyses, we investigated kiwifruit metabolic landscapes at 11 different developmental and ripening stages and revealed a parallel classification of 515 metabolites and their co-expressed genes into 10 distinct metabolic vs gene modules (MM vs GM). Through integrative bioinformatics coupled with functional genomic assays, we constructed a global map and uncovered essential transcriptomic and transcriptional regulatory networks for all major metabolic changes that occurred throughout the kiwifruit growth cycle. Apart from known MM vs GM for metabolites such as soluble sugars, we identified novel transcription factors that regulate the accumulation of procyanidins, vitamin C, and other important metabolites. Our findings thus shed light on the kiwifruit metabolic regulatory network and provide a valuable resource for the designed improvement of kiwifruit quality.

Seaweed Extract as a Biostimulant Agent to Enhance the Fruit Growth, Yield, and Quality of Kiwifruit

The kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson] has attained significant importance for commercial cultivation in the mid-Himalayan region of the Indian subcontinent during the last three decades. The fruit quality matching international standards has remained a concern. Keeping in mind the bio-stimulatory effects of seaweed extract, a marine bioactive component in horticultural crops, the current study conducted to elucidate the impact of seaweed extract on kiwifruit growth, yield, and quality was conducted in the Department of Fruit Science’s kiwifruit block at Dr. Yashwant Singh Parmar University of Horticulture and Forestry, Nauni, Himachal Pradesh, India. For the studies, nine-year-old Allison kiwi vines of uniform size and vigor were planted at a spacing of 4 m × 6 m. With 11 treatments, the experiment was set up in a randomized block design viz, T1: Spray treatment of 1000 ppm (seaweed extract) SWE at fruit set (FS); T2:Spray treatment of 2000 ppm SWE at FS; T3: Spray treatment of 3000 ppm SWE at FS; T4: Spray treatment of 1000 ppm SWE at FS and 10 days after Fruit set (FS); T5: Spray treatment of 2000 ppm SWE at FS and 10 days after FS (DAFS); T6: Spray treatment of 3000 ppm SWE at FS and 10 days after FS; T7: Fruit dip treatment of 1000 ppm SWE at 10 days after FS; T8: Fruit dip treatment @ 2000 ppm SWE at 10 days after FS; T9: Fruit dip treatment @3000 ppm SWE at 10 days after fruit set; T10: Fruit dip treatment @ 5 ppm CPPU at 10 days after fruit set; T11: Control. The current study compared several seaweed extract treatments, which were applied at various times and concentrations, to N-(2-chloro-4-pyridyl)-N-phenyl-urea (CPPU-5ppm) and untreated control. Seaweed extract (SWE) dip at 3000 ppm 10 days after the fruit set produced significant growth in fruit length and diameter in growing kiwifruit, which was non-significant with CPPU treatment and superior to control. The shape index, fruit weight, and total fruit yield were also found to be the highest with the same treatment. Fruit quality parameters, namely fruit soluble solids contents (SSC) and total sugars, were recorded at a maximum with the SWE Spray dose of 3000 ppm at FS and 10 DAFS. The SSC: Acid ratio and reducing sugars were recorded as the highest with an application of SWE dip at 3000 ppm 10 DAFS. The application of SWE dip at 2000 ppm 10 DAFS) was found to advance the harvesting maturity by 6 days and also exhibited the lowest physiological loss in weight (% PLW) with the highest ascorbic acid content. After 15 days of storage at ambient room temperature (25 ± 2 °C), the application of SWE dip at 3000 ppm 10 DAFS recorded the highest SSC acid ratio and the lowest titratable acidity. Thus, the application of seaweed extract dip at 3000 ppm 10 days after the fruit set can be recommended to the farmers as an appropriate alternative to the chemical treatment.

Evaluation of Preharvest Melatonin on Soft Rot and Quality of Kiwifruit Based on Principal Component Analysis.

Botryosphaeria dothidea is the source of the deadly kiwifruit disease known as soft rot. In order to explore the role of melatonin in regulating the postharvest quality and disease resistance of kiwifruit at different growth and development stages, in this study, we applied melatonin at different concentrations to kiwifruit at the young fruit, expansion, and late expansion stages to assess its effect on fruit resistance to B. dothidea, minimize soft rot, and maintain postharvest fruit quality. The results showed that melatonin significantly suppressed the mycelial growth of B. dothidea, with 1.0 mmol/L melatonin inhibiting it by up to 50%. However, 0.1-0.3 mmol/L melatonin had the best control over soft rot. Furthermore, spraying MT during kiwifruit growth can successfully increase fruit weight; preserve postharvest fruit firmness; reduce respiration intensity in the early stages of storage; delay the rise in soluble solids, while maintaining a high titratable acid content to ensure suitable solid acid ratio; increase total phenol, flavonoid, chlorophyll, carotenoid, and ascorbic acid contents; and delay the rise in soluble sugar contents in the late stages of storage. These results have a positive effect on maintaining the nutritional composition of kiwifruit. However, the effects on weight loss, dry matter content, and soluble protein content were not significant. In addition, the results of the principal component analysis demonstrated that 0.3 mmol/L MT increased kiwifruit's resistance to soft rot while preserving postharvest fruit quality.

Antifungal activity and mechanism of tetramycin against Alternaria alternata, the soft rot causing fungi in kiwifruit

Kiwifruit rot caused by the fungus Alternaria alternata occurs in many countries, leading to considerable losses during kiwifruit production. In this study, we evaluated the antifungal activity and mechanism of tetramycin against kiwifruit soft rot caused by Alternaria alternata. Tetramycin exerted antifungal effects through the suppression of mycelial growth, conidial germination, and the pathogenicity of A. alternata. Scanning electron microscopic observations revealed that tetramycin destroyed the mycelial structure, causing the mycelia to twist, shrink, and even break. Furthermore, transmission electron microscopy revealed that tetramycin caused severe plasmolysis and a decrease in cell inclusions, and the cell wall appeared thinner with blurred boundaries. In addition, tetramycin destroyed cell membrane integrity, resulting in the leakage of cellular components such as nucleic acids and proteins in mycelial suspensions. Moreover, tetramycin also caused cell wall lysis by enhancing the activities of chitinase and β-1,3-glucanase and inducing the overexpression of related chitinase gene (Chit) and β-1,3-glucanase gene (β-1,3-glu) in A. alternata. In field trials, tetramycin not only decreased the incidence of kiwifruit rot but also create a beneficial living space for kiwifruit growth. Overall, this study indicated that the application of tetramycin could serve as an alternative measure for the management of kiwifruit rot.

Reasearch on Kiwi Fruit Flower Recognition for Efficient Pollination Based on an Improved YOLOv5 Algorithm

A close relationship has been observed between the growth and development of kiwi fruit and the pollination of the kiwi flower. Flower overlap, flower tilt, and other problems will affect this plant’s pollination success rate. A pollination model based on YOLOv5 was developed to improve the pollination of kiwi flowers. The K-means++ clustering method was used to cluster the anchors closer to the target size, which improved the speed of the algorithm. A convolutional block module attention mechanism was incorporated to improve the extraction accuracy with respect to kiwi flower features and effectively reduce the missed detection and error rates. The optimization of the detection function improves the recognition of flower overlap and the accuracy of flower tilt angle calculation and accurately determines flower coordinates, pollination point coordinates, and pollination angles. The experimental results show that the predicted value of the YOLOv5s model is 96.7% and that its recognition accuracy is the highest. Its mean average precision value is up to 89.1%, its F1 score ratio is 90.12%, and its memory requirements are the smallest (only 20 MB). The YOLOv5s model achieved the highest recognition accuracy as determined through a comparison experiment of the four sets of analysed models, thereby demonstrating its ability to facilitate the efficient target pollination of kiwi flowers.

Spray-drying encapsulation and in-package release of cinnamon leaf essential oil in arabic gum to reduce microbial growth of fresh-cut kiwifruit

Spray-drying encapsulation and in-package release of cinnamon leaf essential oil in arabic gum to reduce microbial growth of fresh-cut kiwifruit

The Plant Growth Regulator 14-OH BR Can Minimize the Application Content of CPPU in Kiwifruit (Actinidia chinensis) ‘Donghong’ and Increase Postharvest Time without Sacrificing the Yield

The application of the plant growth regulator 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) is extensively used for red-fleshed kiwifruits or ‘Donghong’, but it has toxicological properties. Extra plant growth regulators (PGRs) were screened for partial substitution of CPPU (10 mg L−1) to the crops to minimize the CPPU content. The results showed that CPPU at a concentration of 5 mg L−1 plus 14-hydroxylated brassinosteroid (14-OH BR) at a concentration of 0.15 mg L−1 has a nearly equal effect to CPPU at a concentration of 10 mg L−1; it maintains the kiwifruit yields and quality as well as increases the postharvest time. Transcriptome sequencing data revealed that the regulation of 14-OH BR on kiwifruit growth acts mainly by activating Brassinosteroid (BR) signaling to synergistically and antagonistically stimulate the signaling of other endogenous growth regulators, including auxin (IAA), abscisic acid (ABA), cytokinin (CK), gibberellin (GA), jasmonic acid (JA) and ethylene (ET).

Oligosaccharins Used Together with Tebuconazole Enhances Resistance of Kiwifruit against Soft Rot Disease and Improves Its Yield and Quality

Botryosphaeria dothidea is one of the most frequent pathogens of soft rot disease in kiwifruit. The aim of this study was to investigate the role of oligosaccharins used together with tebuconazole to control soft rot and their influences on kiwifruit’s disease resistance, growth and quality. The results show that tebuconazole displayed a toxicity against B. dothidea RF-1 with 0.87 mg kg−1 of EC50 value. Oligosaccharins used together with tebuconazole effectively managed soft rot with 84.83% of the field management effect by spraying tebuconazole + oligosaccharins (0.5:0.5, m/v) as a 5000-fold dilution liquid, which significantly (p < 0.01) exceeded the 72.05%, 52.59%, 62.17% and 33.52% effect of tebuconazole 2500-, oligosaccharins 2500-, tebuconazole 5000- and oligosaccharins 5000-fold liquids, respectively. Simultaneously, co-application of tebuconazole and oligosaccharins was more effective for enhancing the resistance, growth and quality of kiwifruit compared with tebuconazole or oligosaccharins alone. This work highlights that oligosaccharins used together with tebuconazole can be proposed as a practicable measure for managing kiwifruit soft rot and reducing the application of chemical synthetic fungicides.

Genome-Wide Identification and Structural Characterization of Growth-Regulating Factors (GRFs) in Actinida eriantha and Actinidia chinensis.

Growth-regulating factors (GRFs) encode plant-specific transcription factors that play a vital role in regulation of plant growth, development, and stress response. Although GRFs have been identified in various plants, there is no reported work available in Actinidia (commonly known as kiwifruit) so far. In the present study, we identified 22 GRF genes on A. chinensis (hereafter A. chinensis is referred to as Ac, and GRF genes in A. chinensis are referred to as AcGRF) distributed on 17 chromosomes and one contig, and 26 GRF genes in A. eriantha (hereafter A. eriantha is referred to as Ae, and GRF genes in A. eriantha are referred to as AeGRF) distributed on 21 chromosomes. Phylogenetic analysis showed that kiwifruit GRF proteins were clustered into five distinct groups. Additionally, kiwifruit GRFs showed motif composition and gene structure similarities within the same group. Synteny analysis showed that whole-genome duplication played a key role in the expansion of the GRF family in kiwifruit. The higher expression levels of kiwifruit GRFs in young tissues and under stress conditions indicated their regulatory role in kiwifruit growth and development. We observed two genes in Ae (AeGRF6.1, AeGRF6.2) and two genes in Ac (AcGRF6.1, AeGRF6.2) significantly upregulated in different RNA-seq datasets. The presence of conserved protein structures and cis-regulatory elements caused functional divergence in duplicated gene pairs. The subcellular localization indicated the presence of kiwifruit GRFs in the nucleus of the plant cell. Protein-protein interaction analysis predicted AtGIF protein orthologs for AcGRFs and AeGRFs. Taken together, we systematically analyzed the characterization of kiwifruit GRF family members for their potential role in kiwifruit development and Pseudomonas syringae pv. actinidiae (Psa.) invasion response. Further functional studies of kiwifruit GRFs in plant growth, development, and stress response will provide valuable insights for kiwifruit breeders.

Effects of different photovoltaic shading levels on kiwifruit growth, yield and water productivity under “agrivoltaic” system in Southwest China

Agrivoltaic systems (AVS) are emerging mixed production systems where crops are cultivated below the photovoltaic (PV) panels. This study investigated the effects of different PV shading levels on kiwifruit growth, yield and water productivity (WPc), with three densities of 19.0% (T1), 30.4% (T2) and 38.0% (T3) of translucent PV panels installed on the South-oriented AVS roof. The AVS perimeter was left open with the full sun treatment outside the AVS as the control treatment (CKL). Results showed that the solar radiation in T1, T2 and T3 was reduced by 43.8 ± 0.6%, 50.5 ± 0.6% and 55.0 ± 0.5%, respectively, compared with CKL, whereas the air temperature was uniform and the relative humidity increased with increased PV shading. The leaf area index and leaf light use efficiency improved, while the leaf transpiration rate, photosynthetic rate and water use efficiency decreased with increased shading. The accumulated transpiration (T) was higher in CKL (419.9 ± 9.9 mm) than shading treatments (380.8 ± 26.7, 319.2 ± 15.1 and 308.8 ± 12.9 mm in T1, T2 and T3, respectively), and shading also reduced soil evaporation (E) (63.4 ± 1.0, 51.9 ± 3.1 and 47.4 ± 3.8 mm in T1, T2 and T3, respectively, compared to 79.4 ± 1.1 mm in CKL) and thus decreased the total evapotranspiration (ETc act=E + T) requirement. The kiwifruit volume and yield were slightly reduced (−7.3 to 5.5% and −6.5 to −2.6%) in T1 relative to CKL (101.4–106.8 cm3 and 17.6–18.9 t/ha), while the negative effects of shading on the volume and yield were significant (p < 0.05) in T2 and T3. The water productivity (WPc) was improved in T1 (8.2 ± 5.7%) and T2 (5.8 ± 1.9%) relative to CKL, however, it was significantly reduced in T3 (−9.8 ± 1.4%). It was concluded that 19% (T1) PV coverage was a suitable shading treatment management in the AVS, as kiwifruit growth and yield were less affected, and WPc was increased with reduced water consumption. The total potential profit can be largely promoted from electricity production, especially for dry rainfed and no electricity remote areas, where they can benefit from using produced electricity locally for irrigation.

Combining Spectral and Textural Information from UAV RGB Images for Leaf Area Index Monitoring in Kiwifruit Orchard

The use of a fast and accurate unmanned aerial vehicle (UAV) digital camera platform to estimate leaf area index (LAI) of kiwifruit orchard is of great significance for growth, yield estimation, and field management. LAI, as an ideal parameter for estimating vegetation growth, plays a significant role in reflecting crop physiological process and ecosystem function. At present, LAI estimation mainly focuses on winter wheat, corn, soybean, and other food crops; in addition, LAI on forest research is also predominant, but there are few studies on the application of orchards such as kiwifruit. Concerning this study, high-resolution UAV images of three growth stages of kiwifruit orchard were acquired from May to July 2021. The extracted significantly correlated spectral and textural parameters were used to construct univariate and multivariate regression models with LAI measured for corresponding growth stages. The optimal model was selected for LAI estimation and mapping by comparing the stepwise regression (SWR) and random forest regression (RFR). Results showed the model combining texture features was superior to that only based on spectral indices for the prediction accuracy of the modeling set, with the R2 of 0.947 and 0.765, RMSE of 0.048 and 0.102, and nRMSE of 7.99% and 16.81%, respectively. Moreover, the RFR model (R2 = 0.972, RMSE = 0.035, nRMSE = 5.80%) exhibited the best accuracy in estimating LAI, followed by the SWR model (R2 = 0.765, RMSE = 0.102, nRMSE = 16.81%) and univariate linear regression model (R2 = 0.736, RMSE = 0.108, nRMSE = 17.84%). It was concluded that the estimation method based on UAV spectral parameters combined with texture features can provide an effective method for kiwifruit growth process monitoring. It is expected to provide scientific guidance and practical methods for the kiwifruit management in the field for low-cost UAV remote sensing technology to realize large area and high-quality monitoring of kiwifruit growth, thus providing a theoretical basis for kiwifruit growth investigation.

Modelling kiwifruit growth: impact of pollination period on fruit growth dynamic

Modelling kiwifruit growth: impact of pollination period on fruit growth dynamic

Effect of light on growth and chlorophyll development in kiwifruit ex vitro and in vitro

Light is one of the most important environmental factors that strongly mediates plant physiological and morphological development. Few studies have investigated the effect of light on perennial fruit crops, which have long generation times and are large in size, that complicates the evaluation of plant responses to light in controlled environments. This study assessed the impact of light intensity on chlorophyll (Chl) variation in 41 kiwifruit cultivars during the growing season, and examined the physiological, morphological and gene expression changes of kiwifruit plantlets in vitro under different light qualities treatments, such as white light, red light (RL), blue light (BL) and a mixture of RL and BL with different ratios. The Chl content in 24.4% of kiwifruit varieties increased continuously with increasing sunlight intensity from April to August; but 34.15% of varieties remained unchanged and 41.5% of varieties decreased in July and August when kiwifruit plants were exposed to maximum solar radiation density and duration. The controlling experiment of light qualities showed that blue light was effective for the induction and accumulation of kiwifruit Chl contents and carbon nitrogen ratio (C/N ratio), as well as the numbers of guard cell plastids, whereas red light induced plant vegetative growth and increased starch and sucrose content in leaves. Furthermore, blue light induced higher expression of key genes for Chl biosynthesis than red light. These results indicate that kiwifruit plants exhibit strong morphological plasticity induced by light, and the development of kiwifruit can be induced by culturing the plants in vitro under a combination of BL and RL.